1. Field of the Invention
The present invention relates to a heat fixing apparatus used in toner-image forming apparatus, such as copying machines, printers and facsimiles; a tube-coated belt; and an adhesive composition that can be used for the manufacture of a tube-coated belt.
2. Related Background Art
In a heat fixing apparatus generally used in an electrophotography, rotating bodies, such as a pair of heated rollers and a roller, a film and a roller, and a belt and a roller, are pressure-contacted; and a recording material holding toner images before fixation is introduced into a pressure-contacted region formed between the rotating bodies, heated and fused, then cooled and solidified to form permanent images on the recording material.
The rotating bodies to which toner images before fixation held on a recording material contact are referred to as fixation members, and called a fixation roller, a fixation film or a fixation belt depending on their configurations. These fixation members are often formed of a single layer or multiple layers of heat resistant elastic bodies laminated on a base layer formed of a metal or a heat-resistant resin. The outermost layer of a fixation member is called a surface layer, and is formed of a silicone rubber, a fluorine rubber, a fluorine resin or the like. Among them, when a fluorine resin is used for the surface layer, an example of coating with a PFA tube is well known. A structure using a PFA tube through an adhesive layer as the surface layer has also been well known in the art, and a large number of the related techniques have been proposed.
For example, aiming at the surface softness and the thermal conductivity in continuous printing, a fixation roller using a core metal coated with a fluorine resin tube of a thickness of 30 to 50 μm through a silicone-based adhesive of a thickness of 50 to 170 μm has been disclosed (e.g., refer to Japanese Patent Application Laid-Open No. H09-127816).
For improving adhesion durability and elevating accuracy, a PFA tube-coated fixation roller having an elastic layer and an adhesive layer has been disclosed. The adhesive layer is composed of a self-adhesive silicone rubber of a thickness of 3 to 100 μm (e.g., refer to Japanese Patent Application Laid-Open No. 2001-312169).
In order to secure the evenness of adhesion and thickness of an elastic roller having a silicone elastic layer/adhesive layer/fluorine resin coated layer structure, a roller having an adhesive layer formed of a cured product of an additive silicone composition containing an organic silicon compound having selected functional groups, of a thickness of 0.1 to 0.3 mm, has been disclosed (e.g., refer to Japanese Patent Application Laid-Open No. H07-53432).
Furthermore, a method wherein a silicone-rubber layer is formed on a core metal, a self-adhesive silicone rubber, to which an acrylic or methacrylic functional silane coupling agent is added, is applied thereto, and a fluorine resin tube is thermally adhered thereon, has also been disclosed (e.g., refer to Japanese Patent No. 3270489).
In addition, there has also been disclosed a method for manufacturing a tube-coated fixation belt, wherein an additive silicone-rubber adhesive is previously intervened between a rubber-layer coated metal-based belt and a PFA tube, and the adhesive is spread from the outer surface of the tube using a squeezing ring to adjust the thickness of the adhesive layer to be thin (e.g., refer to Japanese Patent Applications Laid-Open No. 2002-36361 and No. 2002-36383).
It has been known that a heat fixing apparatus of a belt-fixation system has a belt-shaped fixation member facilitating to constitute a wide nip and to lower the thermal capacity of the fixation members, and is advantageous for speed raising, energy saving and downsizing of the heat-fixing apparatus. In other words, in order to pass a recording material holding toner images before fixation through the nip portion, and to heat and fuse, then cool and solidify the toner to form permanent images on the recording material, a sufficient quantity of heat must be supplied to the recording material and the toner in the nip portion. Therefore, in order to form permanent images, sufficient surface temperature of the fixation member, and retention time in the nip are required; and in order to achieve high speed, the nip width must be widened to secure a sufficient retention time in the nip.
In the case of the heat-roller fixing, although a method to increase the outer diameter of the roller is used to widen the nip width, this results in the enlargement of the apparatus. Whereas in the fixation apparatus of a belt-fixation system, since the fixation member is belt-shaped, a constitution that can easily secure a wide nip due to a high degree of freedom of shapes can be achieved. Specifically, the belt member is characterized in that a wide nip width to the same outer diameter can be secured compared with the roller member, and is advantageous for downsizing.
For methods of adhering a silicone rubber to a surface fluorine resin layer, adhesiveness and durability at high temperatures are required. A convenient method is the addition of a silane coupling agent in the silicone rubber to impart self-adhesiveness to the silicone rubber itself.
For example, there has been disclosed a method for adhering a fluorine resin tube on the silicone-rubber layer of an elastic roller, such as a fixation roller, wherein a self-adhesive silicone rubber containing an acrylic or methacrylic functional silane coupling agent is used (e.g., refer to Japanese Patent No. 2922712).
There has also been disclosed a method for improving the adhesiveness to a plastic material wherein a combination of an unsaturated-group-containing silane coupling agent and an epoxy-group-containing silane coupling agent is added to a silicone rubber, and an aluminum compound or a zirconium compound is further added thereto (e.g., refer to Japanese Patent No. 3270489).
On the other hand, as an additive silicone-rubber adhesive, an adhesive prepared by adding metal particles to an adhesive containing a resinous organopolysiloxane to control conductive properties has been disclosed (e.g., refer to Japanese Patent Application Laid-Open No. 2002-322363).
When an adhesive layer is formed between the elastic layer and the surface layer, since a roller-type fixation member is generally used without significant deformation, the adhesive layer little undergoes fatigue caused by deformation due to bending or the like, and maintains sufficient adhesiveness; however, since a belt-type fixation member is significantly deformed in operation, large stress is generated between the elastic layer and the surface layer due to bending, which cause a problem of adhesive durability.
Since commercially available silicone-rubber-based adhesives generally contain fillers such as reinforcing silica, they have high viscosities, and are difficult to apply to a thin layer, which cause a problem of poor workability.
Furthermore, in a heat fixing apparatus of a belt-fixation system oriented to downsizing and high-speed operation, since the adhesive layer used in a tube-coated fixation belt is subjected to extensive repetitive bending deformation in operation and easily undergoes fatigue, higher adhesive durability is required.
In a belt coated with a tube having a small diameter oriented to the downsizing of the heat fixing apparatus, the heat-supply time is inevitably short, and the manifestation of the heat supplied from the heat source on the surface of the fixation member delays. Therefore, the surface temperature in the second round is lower than in the first round, and the surface temperature in the third round is lower than in the second round. Thereby, the fixation ability at the leading end and the tailing end of a sheet of recording paper is remarkably lowered, and for example, unevenness of gloss on the recording paper occurs resulting in unsatisfied image quality. Therefore, higher thermal response is demanded. This problem becomes more significant at a process speed exceeding 100 mm/sec, which orients to higher speed.